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How Your Home WorksControl of Heat FlowWithin This PageWhat Does Insulation Do?Insulation is like a giant sleeping bag. It wraps the house in a layer of material that slows the rate at which heat is lost to the great outdoors. Remember that heat always flows from warm to cold, and it moves in three ways: by conduction, convection and radiation. Still air does not conduct heat well and is a relatively good insulator. However, in large spaces such as wall cavities, heat can still be lost across the air space by convection and radiation. Insulation divides the air space into many small pockets of still air; this inhibits heat transfer by convection. At the same time, the insulation material reduces radiation across the space. What Is the Insulation Value?Years ago when the choice of insulation was limited, the measure of insulating effectiveness was thickness. Products have changed, and that rule of thumb can no longer be applied. Insulation is now manufactured and sold by its thermal resistance value (called the "RSI" value) – a precise measurement of resistance to heat flow. The higher the resistance value, the slower the rate of heat transfer through the insulating material. One brand of insulation may be thicker or thinner than another, but if they both have the same RSI value, they will control heat flow equally well. Insulation materials and RSI values
Some insulation materials are marked with both RSI and R-values. RSI values indicate thermal resistance in metric terms (Resistance Système International), and R-values represent imperial measurements. Be careful not to confuse the two. For insulation to work properly, it must be installed properly. There are specific instructions for installing insulation in attics, basements and walls. Some common guidelines, however, apply wherever insulation is installed:
How Much Insulation?Your choice of how much insulation to add will depend on many factors:
Note: Each zone on the map represents an area that experiences a similar number of degree-days. Degree-days are a measure of heating demand based on the difference between the average daily outdoor temperature and 18°C (65°F). Cumulative totals for the month or heating season are used to estimate heating energy needs. The following table is a good guideline to follow to determine insulation levels for different areas of a house.
The following table is a good guideline to follow to determine insulation levels for different areas of a house. You may wish to compare your plans with the Model National Energy Code for Houses for your province or territory. The thermal resistance values listed in the code are more accurate than the ones listed in the table above because they take into account the type of framing and heat loss through the framing materials. You can also obtain information about the recommended minimum levels of insulation that correspond to your home's method of construction, region and heating fuel type. Write to:
Housing Program |
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